Abstract : By analyzing the temperature dependence of the dielectric loss factor/AC conductivity, the activation energy can be determined. Analyses will be presented based upon material type, % of the major phase, density and frequency. Trends in the material's behavior, when placed in a microwave field, can be determined from these analyses. Additionally, from the determination of the temperature at which a material's AC conductivity begins to change rapidly, the onset of a material's change in phase may be indicated, e.g., the onset of sintering. In particular, it has been determined that the dielectric loss constant of Al2O3 has two activation energies, one in the range of .16 to 1. 15 Kcal/mole for low temperatures ( < 700 deg C) and one in the range of 9.22 to 69.2 Kcal/mole for high temperatures ( > 700 deg C) at a frequency of 3.5 GHz and samples from 85% to 100% Al2O3.